Electrical tilt switches and like devices can operate to switch electrical circuits ON and OFF as a function of the angle of inclination of the switch. Such switches normally include a free moving electrically conductive element that contacts at least two terminals when the conductive element moves to an operating position by gravity. A well known form of the electrical tilt switch is the mercury switch. In a typical mercury switch, a glob of mercury moves freely within a housing. As the housing is inclined, gravity pulls the glob of mercury to one end of the housing where it completes an electrical circuit.
Mercury tilt switches are fairly easy to manufacture, however, due to environmental concerns, it is becoming increasingly difficult to manufacture any product that includes mercury. Mercury is a highly toxic substance. As such, there exists a large number of federal, state and local guidelines controlling the use, storage and disposal of mercury. The increase in governmental regulation has increased the cost of manufacturing mercury switches to a point where alternative non-mercury tilt switches have become more competitive.
When manufacturing a tilt switch without mercury, a substitute free moving conductive element must be used. A common substitute is a single metal ball. Tilt switches utilizing metal balls in place of globs of mercury are exemplified in U.S. Pat. Nos. 4,628,160 to Canevari, 4,467,154 to Hill, 4,450,326 to Ledger and 3,706,867 to Raud et al. The use of a metal ball to complete an electric circuit is a simple and inexpensive way to create a tilt switch. However, metal balls do have certain inherent disadvantages. A metal ball contacts a flat surface only along its tangent. Consequently, only a small area of the metal ball is in actual electrically conductive contact within the switch. Adversely, with mercury switches, the mercury glob would envelope a terminal as it contacted it, resulting in a large surface area through which electricity could be conducted. The comparatively small surface area of a metal ball, through which electricity can be conducted, has made metal ball tilt switches less reliable than mercury switches.
Another disadvantage of metal ball tilt switches is that when a metal ball does contact a terminal, the resulting electrical coupling across the contact area is poor. In a mercury switch, the mercury glob would flow into any pit or void it encountered on a terminal, creating a good electrical coupling. However, with metal ball tilt switches, the metal ball is unable to conduct electricity across any pits or voids that exist on either the surface of the terminal or the metal ball itself. Since electricity passes through the metal ball from the terminal it is contacting, arcing can occur across any void in the contact surface. The arcing may cause pitting or corrosion on both the metal ball and the terminal, reducing the conductivity of both surfaces.
It is therefore a primary objective of the present invention to create a more reliable tilt switch utilizing a free moving weight such as a metal ball as the contact element, wherein the contact area between the metal ball and a terminal is increased.
It is yet another objective of the present invention to create a more reliable tilt switch utilizing free moving weight such as a metal ball as the contact element, wherein the pitting and corrosion caused by the arcing of electricity between the metal ball and a terminal is reduced.